A032487 Numbers k such that 221*2^k+1 is prime.

1, 7, 9, 13, 21, 67, 77, 81, 89, 101, 117, 131, 161, 181, 229, 641, 753, 789, 911, 1351, 1461, 1819, 2391, 2951, 4381, 4531, 5633, 6577, 6671, 8521, 10059, 10453, 13571, 15427, 15541, 15969, 16601, 49013, 69831, 118213, 134709, 135281, 180973, 271961, 324567

Offset

1,2

Links

Jeppe Stig Nielsen, Table of n, a(n) for n = 1..52

Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300

Wilfrid Keller, List of primes k.2^n - 1 for k < 300

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

Mathematica

Select[Range[1000], PrimeQ[221*2^# + 1] & ] (* Robert Price, Dec 19 2018 *)

Prog

(PARI) is(n)=ispseudoprime(221*2^n+1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A343001 A297063 A185720 * A332103 A160777 A365986

Adjacent sequences: A032484 A032485 A032486 * A032488 A032489 A032490

Keyword

nonn,hard

Author

N. J. A. Sloane.

Extensions

a(41)-a(51) from the Ray Ballinger and Wilfrid Keller link by Robert Price, Dec 19 2018

Terms moved from Data section to b-file, and new term added to b-file, by Jeppe Stig Nielsen, Apr 19 2020

Status

approved